Process for the extraction of tin from iron alloys



y 5, 1949. J. F. JORDAN 2,474,979

PROCESS FOR THE EXTRACTION OF TIN FROM IRON ALLOYS Filed NOV. 28, 1947 I I mvzmom- Patented July 5, 1949 PROCESS :FOR THE EXTRACTION F TIN FROM IRON ALLOYS llames Fernando Jordan, Huntington Park, Calif.

Application November 28, 1947, Serial .No. 738,425

'3 Claims.

My invention relates to the metallurgy of tin.

Tin metallurgy suffers irom the lack of a simple method of separating tin from iron. I have discovered .such a method. My method consists in extracting tin :irom the solid tin-iron alloy with the solvent. molten lead.

I have discovered that when molten lead contacts a solid tin-iron alloy in the temperature range lying between .the melting point of lead and the melting point of the tin-iron alloy, the tin content of the tin-iron alloy distributes itself between the molten lead and the .solid iron in accordance with .a ratio that apparently reflects the relative solubility of tin in lead and iron at the temperature of the extraction. The tin acts as a solute between the immiscible solvents: molten lead and solid iron.

I carry out my process by first granulating the tin-iron alloy in water; that is, I melt the alloy and pour it into water so as to sub-divide the alloy in a manner that minimizes the cross-section of the individual alloy particles, and thus limits the distance through which the tin must difluse in order to reach the molten lead. Tiniron alloys granulated in water assume a mossy character, similar to the physical form exhibited by mossy zinc; a physical form that I find suitable for my extraction process.

I pack the granulated alloy into :a refractory crucible, such as crucible .II in the figure. With the crucible ll packed full, I lute a cover I by material 8 on the packed crucible ll, pressing cover 1 down firmly on granulated alloy 12 within crucible ll. Through cover"! I pass a refractory pipe 5 that extends nearly to the bottom of crucible ll. Also, I place a "breather opening 6 in cover 1, so as to permit the air within crucible H to be displaced by the molten lead that is to be introduced into crucible 1| thru pipe 5.

With crucible ll packed full of alloy 12, and with cover 1 carefully luted by material 8,1 introduce a stream of hydrogen into crucible ll thru pipe 5. When the air in crucible H is displaced by hydrogen, I heat crucible II and its contents by introducing flame I3 into firing chamber 9, permitting waste gases M to escape in the indicated manner. All the while maintainin a how of hydrogen thru crucible ll, I raise the temperature of crucible H and its contents to a level that lies above -1.000 and below the melting point of the tin-iron alloy. With an alloy containing 10% tin, I raise the temperature of the crucible to about 1800" F.

Alloy I2 is maintained at temperature, in an atmosphere of hydrogen, until all oxide films are removed .from the surfaces of the alloy granules; for, I have found that unless surface films are removed from the granules, my extraction process is not eflicient-may even be prevented from taking place. Ordinarily, one "hour at temperature, in an atmosphere of hydrogen, will remove the surface films sufficiently to permit the molten lead solvent to approach, and contact, the metallic surface of the granules. In any case, complete reduction .of the surface oxides may be checked by testing .for water the hydrogen gas that is escaping through opening (i-the absence of water in the escaping hydrogen indicating that reduction of the oxides within crucible l is complete.

With the surface films removed from granules .l 2, I adjust the temperature of the crucible l I and its contents to the selected extraction temperature. Ordinarily, .I prefer an extraction temperature in the neighborhood of 1800 F. In order to carry out the extraction, I merely pour molten lead into crucible H through pipe 5, see A .in the figure The molten lead fills up the voids between the granules 1.2 within crucible ll, displacing the hydrogen atmosphere within crucible H in .the process, Granules formed by shotting the tiniron alloy in water are ideally suited to permit the molten lead to be introduced into crucible H, for the granules proil'er little resistance to the flow of the molten lead therearound and therebetween. I continue to pour the molten lead into crucible H until the level of the lead reaches opening -6.

With the introduction of molten lead and hydrogen into crucible ll stopped, I now maintain the crucible II and its contents at the selected extraction temperature for eight hours, so as to permit the tin content of the granules to diffuse into the molten lead. An eight-hour extraction periods at 1800 will usually suffice to bring the diffusion process into equilibrium.

When equilibrium is reached, the operation may be completed by cooling crucible H and its contents sufficiently to permit handling, and then transferring the contents of the crucible into a steel-screen filter to separate the detinned granules from the tin-bearing molten lead.

In a test that I made of this process, usin an alloy containing 12.25% tin, formed by alloying pure tin with pure iron, I obtained a tin-lead salloy containing 10.02% tin by treating said tiniron alloy with an equal weight of pure lead at 1800 F. for eight hours. The detinned iron alloy contained, in this test, 2.07% tin-a tin content that could be iurther reduced by repeating the extraction with more pure lead.

The tin-lead alloy produced by my extraction process may be used directly for alloying purposes, or the tin in the alloy may be recovered by employing the conventional Harris reagents.

The absence of non-metallic films on the surface of the tin-iron granules is essential to the success of my process. If the surface film is composed of compounds which are reducible by hydrogen, then the process will be effective if the hydrogen pretreatment is carefully carried out. But if the surface film contains a compound that is not reducible by hydrogen at convenient temperatures, then the hydrogen pretreatment will not suflice, for the unreduced compounds will inhibit the extraction. I have found, for example, that a tin-iron alloy containing silicon responds very poorly to an extraction by the method described. In cases such as this, I modify my extraction process by treating the hydrogen-treated granules with a molten flux that is calculated to remove the surface film that was unaffected by the hydrogen treatment.

In treating tin-iron alloys which possess a resistant surface film, I remove the bulk of the oxide film by treating the granules with hydrogen at 1300 R, or higher. I then lower the temperature of the crucible to around 1000 F., and introduce into crucible H, via pipe 5, molten Zinc chloride-filling the crucible H until the fused chloride overflows opening 6. Opening 6 is specially equipped with a pipe (not shown) that permits the liquid contents of crucible H to overflow without causing a mess. With crucible ll full of the molten fiux, I allow the whole to stand at about 1000 F. for about 30 minutes, whereupon I start to introduce molten lead into crucible ll via pipe 5, permitting the molten zinc chloride fiux to overflow via opening 6 as the molten lead rises within crucible Il. When the molten lead appears at opening 6, the introduction of the lead thru pipe is naturally stopped. Crucible II and its contents are then adjusted to the extraction temperature, and the whole operation continued as usual.

The molten flux employed to remove resistant films need not be restricted to zinc chloride, but may consist of any molten fiux that is capable of performing the required film removal; furthermore, the flux may be caused to replace the hydrogen treatment if desiredthat is, the crucible l l and its contents may be heated above the melting point of the flux, the molten flux added, and, when said flux has removed all films, the operation carried on as usual. However, it must be remembered that a molten flux will not ordinarily remove surface films which are very thick-I, accordingly, find it more satisfactory to remove the bulk of the oxides with hydrogen. I have, on occasion, found it advantageous to add from 5 to 10% sodium fluoride to the zinc chloride flux, in order to improve the attack on silica compounds.

The apparatus shown in the figure is merely one in which I have found it convenient to carry out my process. carrying out my process will occur to those skilled in the metallurgical arts. But whatever the apparatus form may be, the following considerations must be taken into account if success is to be obtained: 1) the extraction will not be successful unless all surface films are removed from the granules, and, once removed, the granules must not be allowed to come into contact with oxidizing gases-such as air or steam; (2) the tin-iron Other forms of apparatus for v ly open to permit the easy inflow of molten flux and lead; (3) the individual alloy granules must possess as thin a cross section as possible, in order to decrease the diffusion distance as much as possible; and, (4), the apparatus must be arranged so that the granules are held beneath the surface to the molten lead, for unless held beneath the surface thereof, said granules will float thereupon.

Having now described and shown my invention, I wish it to be understood that my invention is not to be limited to the specific arrangement of steps herein described and shown, except insofar as such limitations are specified in the appended claims.

I claim as my invention:

1. In the process for extracting tin from a tiniron alloy by means of a molten-lead solvent, the improvement, which comprises: treating said tiniron alloy with hydrogen at a temperature that lies between 1000 F. and the melting point of said tin-iron alloy, so as to remove films from the surface of said tiiviron alloy; treating the hydro gen-treated, tin-iron alloy with molten lead at a temperature that lies between the melting point of said lead and the melting point of said tin-iron alloy; and separating said molten lead from said solid tin-iron alloy after tin has been extracted from said solid tin-iron alloy by said molten lead.

2. In the process for extracting tin from a tiniron alloy by means of a molten-lead solvent, the improvement, which comprises: treating said tiniron alloy with a molten flux that is capable of removing films from the surface of said tin-iron alloy, at a temperature that lies between the melting point of said flux and the melting point of said tin-iron alloy; treating the flux-treated, tiniron alloy with molten lead at a temperature that lies between the melting point of said lead and the melting point of said tin-iron alloy; and separating said molten lead from said solid tin-iron alloy after tin has been extracted from said solid tin-iron alloy by said molten lead.

3. In the process for extracting tin from a tiniron alloy by means of a molten-lead solvent, the improvement, which comprises: treating said tiniron alloy with hydrogen at a temperature that lies between 1000 F. and the melting point of said tin-iron alloy, so as to remove films from the surface of said tin-iron alloy; treating the hydrogentreated, tin-iron alloy with a molten flux that is capable of removing films from the surface of said tin-iron alloy that were not removed by the hydrogen treatment, at a temperature that lies between the melting point of said flux and the melting point of said tin-iron alloy; treating the hydrogen-treated, flux-treated, tin-iron alloy with molten lead at a temperature that lies between the melting point of said lead and the melting point of said tin-iron alloy; and separating said molten lead from said solid tin-iron alloy after tin has been removed from said solid tin-iron a1- loy by said molten lead.

JAMES FERNANDO JORDAN.

REFERENCES CITED The following referemces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 801,290 Witter Oct. 10, 1905 1,479,731 Morgan Jan. 1, 1924 1,562,472 Pedersen Nov. 24, 1925 1,840,708 Fraenkel Jan. 12, 1932 

